There are a number of mobile communication applications requiring precise determination of the position and orientation of a sensing platform. Examples may include directing satellite communication antennas precisely toward geosynchronous satellites, and directing mobile line-of-sight laser or radio communication devices toward each other.
A Global Positioning System (GPS) receiver is a widely used method for determination of position. However, GPS can only determine an azimuth or direction the platform is moving (a heading) by determining the positions of a series of measured locations over time. In some situations, a user may be desirous of maintaining a fixed position.
Laser designators and laser rangefinders can determine a range from a sensing platform position to a remote object. However, these devices may lack the ability to accurately determine a position and azimuth from the reference position to the remote object.
A digital magnetic compass may offer a certain level of azimuth measuring accuracy. However, these devices may be prone to errors caused by perturbations of magnetic interference. A magnetic compass coupled with an Inertial Measurement Unit (IMU) may be less affected by transient magnetic perturbations, but may still be affected by the same magnetic errors and thus limited in accuracy in areas of magnetic fluctuation. Such areas of magnetic fluctuation may include areas of potential desired operation including around large metallic structures and near or in vehicles.
Differential GPS systems can provide a precise solution. However, these systems require two GPS receivers doubling the weight required for an operator to carry into the field.
Some systems may employ two GPS antennas to determine a pointing vector of a system. A dual GPS antenna element system is well-known in the art of differential GPS. Again, as above, two antenna elements increases weight and power in addition to a requirement to continuously receive a signal from a second antenna element.
Dual GPS systems coupled with a magnetic compass may find limited operational precision. As above, external magnetic interference may inhibit an accurate baseline determination between two points.
Additional applications may require radio frequency communications between sensing elements to update position information. For example, a pseudolite may receive a GPS signal and retransmit the received signal to additional receivers in the vicinity. These Radio Frequency (RF) transmissions, however, may undesirably reveal information about the pseudolite including presence, location and origin.
Additional applications may require multiple GPS units to determine a baseline between two locations. A first GPS receiver at the first location may communicate with a second GPS receiver at the second location. Multiple receivers require twice the power, twice the weight, and to be mobile, must be carried, often in a backpack.
Should the remote position be dangerous to the user, current limitations in mobility may drive users to a more distant reference position. If a user must evacuate the reference position due to unforeseen events, current cumbersome devices may inhibit movement. Also current cumbersome devices, if discarded, may contain sensitive information the user may not desire to share.
Therefore, a need remains for a mobile device and system enabling precise determination of a baseline from a fixed point in space using a single antenna with a single GPS receiver.